Construction of Maryland's Purple Line light-rail transit system will continue as scheduled, at least for now, following a federal appeals court ruling that frees Maryland from having to update the project's environmental studies.

Opponents of the $5.6-billion public-private project, sited in the Washington, D.C., suburbs, challenged the validity of the state's ridership projections, claiming they did not account for declining ridership on the regional Metrorail transit system. After service begins in 2022, transfers between the two systems at four stations will provide as much as 27% of the Purple Line's passenger totals.

The three-judge panel rejected the plaintiffs' claims in an opinion released on Dec. 19, finding that the analyses met all legal tests for the project to continue. The case had delayed the Purple Line's originally scheduled August 2016 start of construction by more than a year and nearly forced the project's cancellation in mid-summer, before a circuit judge allowed construction to get underway pending a ruling. Groundbreaking ceremonies finally were held on Aug. 27.

Although the case is unlikely to be appealed to the U.S. Supreme Court, the Purple Line's days in court are not over. Opponents have challenged the legality of the project's $900-million FTA New Starts grant, given the current shortfalls among the region's governments to fund Metrorail operations and maintenance.